Safety switch



March 2, 1954 J. H. scHELLMAN SAFETY SWITCH Filed April 2, 1951 5 Sheets-Sheet l M. @nl l; Y gli ATTORNEYS.

March 2, 1954 J. H. scHELLMAN SAFETY SWITCH Filed April 2, 1951 5 Sheets-Sheet 2 NVENTOR Jose/a f7. Scglmm.

ATTORNEYS. i

March 2, 1954 Filed April 2, 1951 J. H. SCHELLMAN SAFETY SWITCH 5 .Sheets-Sheetl I5 March 2, 1954 J. H. scHELLMAN SAFETY SWITCH' 4 u 3. m e

M 8 w w /i d 4 e, W l M H e@ Y, f r m l I I fl ,E II w .7 Hh o. m 2 d 0 /l 7 e 2 m w W www INVENTOR Josep/z l1'. clzellmaxz.

ATTO R N EYS March 2, 1954 .1. H. SCHELLMAN 2,671,140

SAFETY SWITCH Filed April 2, 1951 5 Sheets-Sheet 5 f' X ATTORNEYSE Patented Mar. 2, 1954 SAFETY SWITCH Y Joseph H. Schellman, Ridley Park, Pa., assignor to Hetherington, Inc., poration of Delaware Sharon Hill,

Pa., a cor- Application April 2, 1951, Serial N o. 218,816

(Cl. ZOO- 77) 17 Claims.

The present invention 'relates to electric switches, particularly of the type which Vmake instantaneous contact, as for example to operate mechanism on an airplane or the like.

A purpose of the invention is to provide protection against welding or freezing of electric contacts, particularly in the case of control mechanism.

A further purpose is to provide for completion of two sets of electric contacts in series in the forward motion of a plunger and provide for breaking both sets in retraction, and in any case for breaking one set in case the other will not break on account of welding.

A further purpose is to place one or more self-adjusting movable contacts on the plunger in series with the shorting contact closed by a hill and valley projection on the plunger.

' A further purpose is to mount the self-adjusting movable contact or contacts on a self-adjusting movable contact carrier which has lost motion with respect to theplunger, preferably due to the action of a spring in urging the self-adjusting movable contact carrier against a shoulder on the plunger.

A further purpose is to provide a self-adjustmovable contact on a plunger which engages the fixed contact and which is electrically connected in a circuit by the shorting contact which closes against the self-adjusting movable contact or other Contact in electrical connection with the self-adjusting movable contact.

A further purpose is to bring a plurality of electrically separate self-adjusting movable contacts forward on the self-adjusting movable contact carrier of a plunger into engagement respectively with fixed contacts, and then to interconnect the self-adjusting movable contacts while they are connected to the xed contacts by movement of the shorting bar carrying the shorting Contact under the action of a hill and valley projection on the plunger.

A further purpose is to bring a self-adjusting movable Contact in lost motion relationship with the plunger into contact with a fixed contact and then by reverse motion of the shorting bar over the hilland valley projection to interconnect the self-adjusting movable contact while engaged with the fixed contact to a plurality of other ixed contacts inwardly extending into the path of the snorting Contact.

A further purpose is to make iixed contact connection with the plunger itself, which is of electrically conducting material.

Agfurther purposeis to extend a locating ear from the self-adjusting movable contact carrier 55 between f xed contacts to maintain the relationship of the self-adjusting movable contact or contacts to the fixed contacts.

A further purpose is to provide auxiliary contacts which will complete a circuit on further forward motion of the plunger when the circuit is not completed on initial forward motion.

A further purpose is to provide rearwardly directed xed contacts which are engaged by self-adjusting movable contacts and forwardly directed xed contacts which are engaged by the shorting bar, and to interconnect one of the rearwardly directed contacts with one of the forwardly directed contacts.

A further purpose is to provideA a iirst selfadjusting movable carrier and self-adjusting movable contacts and a snorting bar, which together complete contacts in series on an initial forward motion of the plunger, and to provide an auxiliary self-adjusting movable carrier and contacts which complete the circuit on further forward motion of the plunger notwithstanding the failure of the shorting bar to operate.

A further purpose is to provide opposed plunger switches with a lost motion connection between them, having only sufficient freedom to permit one switch to operate at a time, so that in case of closing motion on one switch the other switch is forced open.

A further purpose is to provide a lever interconnection between the plungers of switches arranged side by side which will force open one switch when another switch is closed.

A further purpose is to make the lever interconnection universal in action so that a plurality of switches will interlock to permit the closing of one switch to force open an opposite switch.

Further purposes appear in the speciiicatlon and in the claims.

In the drawings I have chosen to illustrate a few only of the numerous embodiments in which my invention may appear, selecting the forms shown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

Figures l to 3 show the preferred embodiment.

Figure 1 is an axial section (through the axis of the plunger) of the preferred form, the switch being in open position.

Figure 2 is a View similar the switch partially closed.

Figure 3 is a view similar to Figure l, showing the switch fully closed.

Figure 4 is a section on the line 4 4 of Figure 1, the switch being open.

Figure 5 is a section on the line 5-5 of Figure 2.

to Figure l, showing Figure 6 is a bottom plan view of Figure 1.

Figure 7 is a bottom plan view of the selfadjusting movable contact carrier of Figures 1 to 6.

Figure 8 is a perspective of the shorting bar, omitting the snorting contact and springs.

Figures 9 to 15 inclusive show a variant embodiment of the switch of the invention.

Figure 9 is an axial section through the case on the line 9 9 of Figure 13, with the selfadjusting movable contact carrier and fixed contact block shown in elevation and the switch in open position.

Figure 10 is a section on the line IE-i of Figure 13 showing the switch partially closed.

Figure 11 is a View similar to Figure 10 with the lower portion of the case shown in elevation and the switch fully closed.

Figure 12 is a section on the line iii-l2 of Figure 9.

Figure 13 is a section on the Figure 9.

Figure 14 is a bottom plan view of Figure 9.

Figure 15 is a bottom plan view of the selfadjusting movable contact carrier of Figures 9 to 13.

Figures 16 to 20 illustrate a further variation in the switch of the invention.

Figure 16 is an axial section through the switch of this variation, in open position.

Figure 17 is a section on the line ii--i'l of Figure 16, in open position.

Figure 18 is a section on the line Figure 16.

Figure 19 is a bottom plan view of the fixed contact block of Figures 16 to 18.

Figure 20 is a top plan view of the main selfadjusting movable contact carried and the auxiliary self-adjusting movable contact carrier of Figures 16 to 19.

Figure 21 is an axial section through the outer case of the preferred embodiment of interlock applied to the switches of the invention.

Figures 22 to 24 illustrate a further interlock embodiment.

Figure 22 is an axial section showing one of the switches in elevation.

Figure 23 is a section on the line 23-23 of Figure 22.

Figure 24 is a bottom plan View of Figure `22.

Figures 25 to 27 illustrate a further variation of interlock.

Figure 25 is an axial section in open position.

Figure 26 is a top plan View of Figure 25.

Figure 27 is a section on the line 21-21 of Figure 25.

Describing in illustration but not in limitation and referring to the drawings:

Switches of the instantaneous contact variety such as push button switches and instantaneous contact rocker and toggle switches are widely used, particularly in aircraft applications. Such switches iind very important applications especially in aircraft, where they constitute the main actuating switches for trim tab circuits (trimmer ailerons), gun and rocket ring circuits, drop tank circuits and numerous other control and signal circuits. It will readily be understood that the proper functioning of such switches is critical both to the safety of the airplane or other equipment and to the proper performance of the machine. Y

Difficulty has been encountered, through the tendency of such switches to freeze or weld closed on making contact, or to fail to make contact.

line lS-l of iS-8 of Either condition may be serious or fatal in the operation of the airplane or other equipment.

By the present invention it is possible to assure the breaking of a vital circuit notwithstanding that one set of contacts may freeze or weld.

It is also possible by the present invention to close a circuit by forward movement of the plunger notwithstanding that one set of contacts may fail to close. The present invention also makes it possible to apply a counter dislodging force to break the connection of contacts which may have welded or frozen closed.

While the invention is believed to have its widest application in instantaneous contact aircraft switches, it will be understood that it can also be applied to switches employed in other applications and is by no means limited either to aircraft or to instantaneous switches.

Considering first the form of Figures 1 to 8 inclusive, I there illustrate a plunger switch having a suitable outer metallic case 36, desirably of circular cross section, 'having an externally threaded stem 3| of well known character which is intended to pass through and suitably thread in an opening 32 through a panel 33 (which may be the instrument panel of an airplane). The stem is held in place and the switch is positioned by opposed nuts 34 and 35 acting on a washer' Bt against the outside of the panel.

The stem 3l has passing through the centera push button opening 31 which is provided with a forwardly directed shoulder 33. A push button or actuating member 4l] passes through the opening 31 and has a shoulder 4I near its inner end which engages against the shoulder 38 in the stem in retracted position and prevents dislodgment of the push button from the stem.

In the form of Figures 1 to 8 the push button is suitably of insulating material as shown, but it will be understood that it can be slightly modified to aid the grip and made of metal if desired, as shown in MI inFigures 16 and 17.

The push button is desirably rigid with and effectively a part of switch plungerrli? which extends down the center of the switch as later explained. The plunger is preferably made of metal, and for the purpose of joining with the plastic push button is provided with a rear end boss 43 which is imbedded in the plastic and a slightly forward boss 44 which conforms to the interior cylindrical cross section of a spring recess 45 which extends inside the push button around the plunger.

Forwardly of the boss 44, the plunger has a uniform lost motion sliding portion i6 which is surrounded and engaged by a loose freely-longitudinally-movable self-adjusting movable contact carrier 41. The self-adjusting movable contact carrier is suitably recessed at it forwardly and the end of the recess engages a rearwardly directed shoulder formed by a rim on the plunger which forwardly terminates the lost motion sliding portion 46. l

Rearwardly directed from the self-adjusting movable contact carrier, immediately around the plunger, is a rim 5l on the self-adjusting movable contact carrier which guides the inside of a lost motion spring 52 in the spring recess 45 extending from the push button at the rearward end to the self-adjusting movable contact carrier at the forward end.

The self-adjusting movable contact carrier in this form is of electrical insulation material such as phenolic plastic, and has at circumferentially spaced points on'its forward surfaces v(suitably springabutment at onevend and bythe diametrally opposite position), movable contacts 53l and154 'of any material having good electric conductivity, preferably silver. The self-adjustingmovable contacts are desirably placedby imbedding in the plastic.

In line with tne'respectve self-adjusting'movable contacts and positioned-forwardly yoftnem are rearwardlyy directed fixed contacts 55 and 56 suitably provided'witn terminal ends 5l to permit direct solder connection-to the ends. The terminal ends yare desirably imbedded in al plastic or other suitable insulating block 58, secured in the forward open end of the casing 30. An insulating sleeve Ell on the inside of the casing surrounds the `self-'adjusting movable contact carrier and the rearwardly directed ends of the xed contacts.

' A locating ear 41 from the self-adjusting movable contact carrier of plastic extends down between xed contacts. 55 and 56 and guides the self-adjusting movable contact carrier against turning so that the self-adjusting movable contacts would not register with the xecl contacts.

The plunger has a hill and valley projection 6l located forwardly of the shoulder 5L?, and a shorting bar 62 of any well known character surrounds the plunger and rides over the hill and valley projection.

The snorting bar 62 desirably comprises a U- snaped metallic strip B3 (Figure 8) having an opening 64 in the center of the base of the U, large venough to pass over the hill and valley projection. The arms 55 of the U extend forwardly and in the inactive position engage an abutment surface 65 (Figure 3) on the insulating block 58, which limits the forward motion of the snorting bar and pushes the snorting har over the hill and valley projection when the plunger moves forward. On'the opposite sides of the plunger, generally straight spiral springs G5 extend across the snorting bar and are held inside the U of the snorting har and in spring ein gagement with the plunger by ears Gl' from the arms 65, which extend inwardly and restrict the ends of the springs as best seen in Figure 8.

Forwardly of the springs, the snorting har has a transverse insulating plate 8 (Figure 2) provided with a hole 'l0 at the center, large enough to over the hill and valley projection, and held in place by ears 1| 65 of the U, which engage at the corners of the insulating platev with interfitting projections on the insulating plate fitting in the recesses formed by ears 1l.

- self-adjusting `Cm the side of the snorting bar, directed toward tne'self-adjusting movable contacts, a disc-like snorting contact l2 is located, secured to the snorting bar as by welding. The snorting contact is of. any suitable Contact material, such as silver. The radial extent of the snorting contact 'l2 and of the other parts of the snorting bar is limited so that they will. not touch the fixed contacts as the .snorting har moves back and forth, but is great enough so that the shorting contact will engage, and in the form of Figures 1 to 8 will bridge, .theself-adjusting movable contacts when the snorting bar moves rearwardly over the nill-and-valley projection.

At the forward end the plunger has a spring abutment or collar VI3 and a spring stem 'T4 which engages inside a 'plungerretraction .compression spring T5 in a vspringr well 18: in the insulating block 58. Retracting spring is engaged bythe bottom-of (Figure 8) from the arms c tacts. On the other hand, if welding thea-well at the 'otherend and is guided by the spring stem I4 inside-the spring.

Atv theioutside ofthe switch, ribs 'l1 of insulation suitably integral with the insulating block extend across the 'block between the xed contact terminals.

"In operation, when the user presses the push button to depresstne plunger, the plunger starts from its rearward position with the snorting bar forward against the abutment S5 onthe insulatingtblock and the lost motion of the self-adjustingy movablev contact carrier taken up. The plungerV andvself-adjusting movable contact carrier moveL forward togetneras a unit to the positionl shown in Figure 2, at which position the self-adjusting movable contact or contacts on the self-adjusting movable contact carrier engages the xed contact or vvcontacts and to that extent completes the circuit. In the preferred embodiment, however, whcnthe self-adjusting movable contactsengage the xed contacts, the hill-andvalley projection has not yet moved far enough forward in the snorting bar to trip the snorting bar and make it move rearwardly against the self-adjusting movable contacts. On further forward motion `.of the plunger, as shown in Figure 3, however, the snorting bar is tripped as well known and moves rearwardly along the plunger over the nill-and-valley projection with a snap action, until the snorting contact engages tne self-adjusting movable contacts, at which point the circuit is completed. Thus current flows from one fixed contact to the cooperating self-adjusting movable contact, to the snorting contact, to the other self-adjusting movable contact and thence to the other fixed contact. The self-adjusting movable contacts in this case complete the circuit between each xed Contact and the snorting contact.

When the pressure by the user on the plunger is relaxed and tnevplunger retracts under the action of the retracting spring and the self-adjusting movable lost motion spring, the plunger moves rearwardly while the snorting bar is held by the engagement of the snorting contact with the self-adjusting movable contacts. First, the hill-and-valley projection retracts through the snorting bar until the snorting contact is tripped and snaps in the forward direction over the nilland-valley projection to the position of Figure 2. This snap action breaks the circuit and breaks any arc. On further retraction of the plunger, the lost motion between the self-adjusting movable contact o --rricr and the plunger is taken up until the self-adjusting movable contact carrier has engaged the rearwardly directed shoulder 58 on tne'plunger, after which the selfadjusting movable `Contact carrier and self-adjusting movable contacts Vmove rearwardly with the plunger on further retraction to the position of Figure 1, breaking the electrical connection between the self-adjusting movable contacts and the` fixed contacts.

In case eitnerset of contacts welds or freezes when the circuit is made, the circuit can nevertheless be broken by the other set of contacts. Thus if the snorting contact welds or freezes at either side to one of the self-adjusting movable contacts, the retraction of the plunger will nevertheless break the-circuit between the selfadjusting movable contact the ccnor freezing occurs Vbetween either of the fixed contacts, and the corresponding self-adjusting movable ccntachtne circuitl is broken bythe snorting contact Ainto a position between two of fixed contact 55', as shown in Figure 7 when the snorting bar moves forward on the hilland-valley projection. This effect is made possible by the fact that the respective contacts are connected in series.

The form of Figures 1 to 8 employs a plurality of contacts completing a single circuit in series. In the form of Figures 9 to 15 which is generally similar, a plurality of contacts in series complete the circuit to serve diiierent branches by connecting to a number of diierent terminals. In this case the self-adjusting movable contact carrier, which is generally similar to that already described, and mounted on a similar plunger, supports a single shelf-adjusting movable contact 53, which in forward position as shown in Figures 10 and 11 engages a single fixed contact 55 provided with a suitable terminal connection on the outside of the insulating block 58'.

The shorting bar in the form of Figures 9 to is desirably the same as that of Figures 1 to 8. A plurality of L-shaped iixed contacts, in the present instance 18 and 80, are mounted in the insulating block 58 in insulated relation, and have inwardly directed ends 8l, whose forward edge is at the same forward position as the forward edge of the self-adjusting movable contact when it engages iixed contact 55'. Contacts 1S and 8B are provided with suitable external terminals as shown. The locating ear 412 on the self-adjusting movable contact carrier extends the fixed contacts and guides thereon t-o prevent relative turning of the self-adjusting movable contact carrier as it moves back and forth. Thislocating ear, like the self-adjusting movable contact carrier, is of insulating material in this form.

In the form of Figures 9 to 15, a metallic contact 82 at the forward end around the plunger and retracting spring conforms to the shape of the spring well and through the retracting spring 15 makes electrical contact with nthe plunger (which is of electrically conducting material) and through the shorting bar springs makes electrical connection with the shorting contact.

In operation in this form, the self-adjusting movable contact carrier is fully rearward and the shorting bar fully forward so that the switch is open in Figure 9. The pressure of the finger on the push button moves the plunger forward until the self-adjusting movable contact 53 vengages 10. At that point the self-adjusting movable contact and self-adjusting movable contact carrier cease to move forward and lost motion is taken up as the plunger moves forward. In the position of Figure 10 the hill-and-valley projection has not yet moved far enough forward to trip the shorting bar and the snorting bar is in its forward or inactive position. l v

On further forward motion of the plunger, as in Figure 11, the hill-and-valley projection moves to the other side of the shortingbar springs and the snorting bar is tripped and moves rearwardly, until the snorting contact engages the selfadjusting movable and the inwardly projecting ends 8| of fixed contacts 18 and 8U.

At this point it will be observed that common circuit connections are made from separate branches represented by iixed contacts 18, 8B and 82 with fixed contact 55'` the circuit connections in each case being completed throughthe shorting bar and the self-adjusting movable contact.

On retraction of the plunger, the snorting bar is rst tripped to its inactive or forward position,

8. breaking the circuit between fixed contacts 18, and 82 respectively and the self-adjusting movable contact. On further retraction of the plunger the lost motion between the self-adjusting movable contact carrier and the plunger having been taken up, the self-adjusting movable contact carrier and self-adjusting movable contact move rearwardly with the plunger, breaking the circuit between fixed contact 55' and the self-adjusting movable contact.

If either of the contact-making means welds or freezes, the other can break the circuit by retraction. Thus if any of the contacts made by the'shorting bar welds or freezes, the circuit is nevertheless broken on retraction oi the plunger by separation of the self-adjusting movable contact from fixed contact 55' (which will normally be connected to the source of power at the positive side in a direct current circuit). Likewise, if welding or freezing occurs between the self-adjusting movable contact and iixed contact 55', the circuit is nevertheless broken by the shorting contact. In both of the forms above described, the retracting spring will ordinarily be relatively weak while the lost motion spring will ordinarily be stronger.

In some cases it is desirable to have emergency contact making means as well as emergency contact breaking means.

In the form of Figures 16 to 20 inclusive, the plunger @2' has a pin 43 imbedded in the push button. An insulating bushing 60 is on the inside of the casing. A lost motion stem'li extends forwardly and then joins a further forwardly extending reduced second lost motion stem 452, having a rearwardly directed shoulder 4S. A main self-adjusting movable contact carrier 33 surrounds the lost motion stem 46 and has a rearward skirt-like extension 8d which rides along it. Unlike the previous self-adjusting movable contact carriers, this self-adjusting movable contact carrier is metallic and electrically conducting and carries self-adjusting movable contacts 53 and 54', suitably at diametrally opposite positions. Extending across at the center, selfadjusting movable contact carrier 83 is recessed at 84 to form a cruciforrn arrangement and across this recess extends auxiliary self-adjusting movable contact carrier 85, which in its forwardmost position rests against rearwardly directed abutment 85. Self-adjusting movable contact carrier 85 is also metallic and electrically conducting and has diametrally opposite contacts 8S and 81 which are disposed 90 from contacts 53 and 54. An opening 8S in selfadjusting movable contact carrier 55 conforms in slidable relationship with lost motion stem 462. The auxiliary self-adjustingmovable contact carrier is urged forwardly against abutment 48 by 10st motion spring 90 which acts between a forward shoulder El on the plunger and the self-adjusting movable contact carrier around lost motion stem 462. For the purpose of getting the auxiliary.self-adjusting movable contact carrier and lost motion spring in place, the plunger may be made up in several pieces, threaded or otherwise united as well known.

The rear edge of auxiliary self-adjusting movable contact carrier 85 forms a rearward abutment 92 which normally engages main self-adjusting movable contact carrier 83. The main self-adjusting movable contact carrier is urged against abutment 92 by lost motion spring 93 acting between washer 94 surrounding the plunger forward of the push button and the rear edge of the self-adjusting movable .contactcarrier 83. Skirt 84 guides the spring.

Both of the self-adjusting movable .contact carriers are diametrally within the case, and an insulating lining 60 at the rearward end and inside of the case prevents electrical contact with the case.

The shorting bar, 62' in the form of Figures I0 to 20, is slightly different from that previously shown, and employs a ring 95 large enough to move over the hill-and-valley projection, having an annular external recessV 9.5 which receives a spiral garter tension spring 91 which pushes a ball 98 into a ball recess |00 at one portion oi the circumference so that the ball rides the hilland-valley projection rather than the spring directly. A snorting contact I2 suitably of silver, is mounted on the rearward 'face of the snorting bar and suitably is an annulus. The shorting bar is engaged by an abutment on the insulating block 582 which closes the forward end of the casing and inwardly insulates the casing wall from the shorting bar by a skirt.

The forward end of the plunger is inwardly recessed at I| to receive a retraction compression spring 10 which extends from the bottom of the recess at one end to the bottom of spring well 'l5' in the insulating block 582.

Provision is made for lost motion between the rearward and forward portions of the plunger by extending a stem |02 of the rearward portion into a recess |03 in the forward hill-and-valley portion. A lost motion compression spring |04 extends from a shoulder 05 on .the rearward portion to a washer |06 around the stem |02 engaging the forward portion. The washer is, in inactive position of the switch, urged by the retracting spring against ya shoulder |01 in a recess I 08 of a fixed contact block ||0 secured in the middle of the casing and positioned by the skirt portions of the insulations at the opposite ends.

The insulating block |I0 supports a number of xed contacts. A rearwardly directed iixed contact I I cooperating with self-adjusting movable contact 53" and covering a segment less than .90 is electrically connected to an external terminal ||2 which is insulated from the casing by bushing |I3. The opposite self-adjusting movable contact 54 cooperates 'with rearwardly directed fixed contact ||4 which suitably extends almost metallic rivet I I5 to a forwardly `directed xed contact I I6 on the opposite side of the xed contact block which also suitably covers slightly less than 180 as shown in Figure I 9, and which cooperates with the shorting contact 72. Positioned 90 from xed contact I and rearwardly directed is iixed contact II'I which is connected to an external terminal |I8 and insulated from the case by bushing |20. Fixed contact |I7 is contact I2| as by rivet |22. Fixed contact |2| also desirably extends slightly less than 180 and cooperates with the shorting bar.

In operation of the form of Figures 16 to 26, when the user presses onl the push button Mland forward, the rearward portion of the plunger begins to `move forward, .carrying with it the main and auxiliary self-adjusting movable contact carriers, but thezhill-and-valley ferred embodiment. As the rearward portion of the plunger moves forward, self-adjusting movable contacts 53' and 54 make electrical connection respectively with rearwardly directed fixed contacts and H4. Since contacts ||4 and IIG are electrically connected by rivet ||5, the electrically conducting self-adjusting movable contact carrier 83 has thus made electrical connection with xed contacts iii, H and IIS. Further forward motion of the plunger takes up lost motion with self-adjusting movable contact carrier Sli and compresses plunger compressing spring By this time the lost motion between the rearward and forward portions of the plunger has been taken up by compressing spring |04 and further forward motion of the plunger causes the hill-and-valley projection to move forward with the rearward portion of the plunger. This brings the ball Sil to the other side of the hilland-valley projection and causes the shorting bar to snap rearwardly on the plunger, bringing the shorting contact into electrical connection with the forwardly directed xed contacts IIB and l2|- As a result contact IZI is connected to the other contacts and since it is electrically connected by rivet E22 with the body of Contact II'I, the circuit is completed from terminal ||2 to terminal |I8. In breaking the circuit the action is exactly like thatI of the other forms already described, the snorting bar rst snapping forwardly to break connection between forward directed contacts ile and |25 and then the selfadjusting movable contact carrier 83 moving rearwardly to the position shown in Figure 16. If the snorting contact becomes welded or frozen, self-adjusting movable contact carrier still breaks the circuit. If one of the self-adjusting movable contacts 53 or 5d becomes frozen or welded, the shorting bar still breaks the circuit.

During all of this operation the auxiliary selfadjusting movable contact carrier has been inactive. If, however, the shorting bar should fail 1 example due to breaking of its spring or clogging of its parts with dust or the like, it is still possible t0 complete the circuit by pushing the plunger still further forward until self-adjusting movable contacts 86 and 81 on auxiliary self-adjusting movable contact carrier make electrical connection across from rearwardly directed fixed contact IM to rearwardly directed fixed contact lil. In this instance an auxiliary circuit is made to replace the shorting bar circuit from iixed Contact III te selfadjusting movable contact 53 through self-adjusting movable contact carrier 83 which is electrically conducting) self-adjusting movable contact Sii', to fixed contact I I, to auxiliary selfadjusting movable contact 87, to auxiliary selfadjusting movable contact carrier f5 (which is electrically conducting), to auxiliary self-adjusting movable contact St, to xed contact |Il'.

In some instances it is not sufcient merely to provide auxiliary contacts for making and breaking the circuit, but is very desirable also to be able to exert a pushing action on the plunger to dislodge the plunger when it sticks. The forms of Figures 21 to 27 illustrate dii-ferent ways in which this can be accomplished.

The form of Figure 21 is particularly suitable for trim 'tab switches or other switching installations where two switches move the same element in opposite directions or in opposite manner. In this form a frame |23 has opposed switch pockets |20 and I 25 which receivev plunger switches, which maybe of any suitableV character, whether prior art plunger switches or switches of the character shown therein, but are shown as being the switches of Figures 1 to 8 inclusive. One switch has an extension on its plunger through the rear, which carries an abutment |26, and on the other plunger carries a U-shaped socket |21 which receives the abutment. The plungers are preferably co-axial so that the forces are directly in line. The lost motion between the abutment and bottom of thc socket is sufficient to close one switch, but insufficient to permit the other switch to close also. Accordingly, if the left hand switch in Figure 21 is closed and the lost motion is taken up, and the plunger of that switch sticks, the plunger can be dislodged by pressing on the push button 43 of the right hand switch, which exerts pressure from the socket 521 to the abutment |26. It will be evident that it is diilicult to supply a substantial pulling force on the push buttons, but that a pushing force or tapping action can be exerted from the other switch in this manner.

In the form of Figures 22 to 24 the reverse action is exerted on the plungers by a lever. In this form a double switch housing |28 mounts two plunger switches |36 and |31, suitably of the character shown in Figures 1 to 8. Instead of the usual push button, hemispherical heads |32 are mounted on the plungers, and in retracted position the shoulders il on the heads engage in shoulders 3B of openings 52 in a mounting plate |33 extending across the housing. The mounting plate at the middle supports a pivot |34 on which a rocker |35 extending across and engaging the respective heads |32, is duly pivoted. An operating handle |35 extends through an opening 31 in the front of the switch, and permits the operator by rocking the handle to depress either one of the switches.

An insulating sleeve |3t surrounds the switches on the inside of the casing.

The fixed contacts of both switches are mounted on an insulating block |46 which holds the contacts in the relationship shown in Figures 1 to 8 inclusive. Each of the plungers has a forward extension I4! threaded on the end at |42 beyond the projection, and provided with a forward shoulder 13 which engages the rearward end of the retraction spring 16 in the spring well 15. The plunger extension passes through an opening |43 in the insulating block |46 and b..- yond the forward end of the block engages one end of an interlock lever |44 pivoted at |65 on a fulcrum |46 mounted on the block |46. There is only sufficient lost motion between the plungers and the interlock lever |44 to permit one switch to move to closed position at a time and as soon as one switch moves to closed position the opposite end of the interlock lever pushes rearwardly on the plunger of the other switch, thus exerting a positive dislodging force to reduce any weld or obstruction. Thus, if the functioning of a particular switch is impaired, the user can momentarily close the opposite switch of the pair and by doing so can correct the malfunctioning of the switch which is not properly operating.

The features shown in the form of Figures 22 to 24 are embodied in the form of Figures 25 to 21, which shows a four-switch group consisting of switches |41, H48, |50 and |5l, each suitably like the construction of Figures l to 8 inclusive, mounted in an insulating casing |52 at 90 circumferential spacing. The outer fixed contacts extend up at |53 adjoining the insulating casing, while the inter fixed contacts |54 in this case are connected to a common terminal post |55, placing all of the switches in branches of the same circuit. A ball |56 at the face of the housing is supported by a threaded stud |51 in a threaded opening |58 of the cover |60. A switch operating rocker |6|, suitably of insulation, has a socket |62 which makes universal joint mounting on the ball and has an annular lever ange |63 which engages the button heads of all the switches. The motion of the lever |5| can be confined to the four directions required to move the four switches by a cruciform slot in the panel as well known (not shown).

The stud |51 is extended and receives a universal joint spherical surface pivot bearing |64 which pivotally mounts an interlock plate |65 having an opening passing the stud and having fork ends |66 which engage around each plunger and the spring 52, between the push button head and the self-adjusting movable contact carrier.

In operation it will be evident that whenever the rocker |6| is rocked in the direction to close one of the switches, the corresponding end of the interlock plate is moved forwardly and the opposite end of the interlock plate is moved rearwardly, exerting a dislodging or retracting force on the interlock spring and through it on the plunger to dislodge the opposite switch. By this means any switch which sticks can readily be released. .Also when one switch is closed, the interlock moves forward at that switch position and moves backward at the other switch positions, preventing the other switches from closing by engaging under their button head.

It will be evident that by the invention additional safety precautions are provided against damage to an airplane or other equipment through failure of control switching. These precautions take the form of provision for breaking a circuit in case an individual set of contacts stick, and also for closing a circuit in case an individual set of contacts fail and for releasing a sticking plunger. Y

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benets of my invention without copying the structure shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patentis:

1. In a switch, a plunger, a self-adjusting movable contact carrier on the plunger, a contact mounted on the contact carrier, a fixed contact engaged by the contact on the contact carrier during forward movement, a hill-andvalley projection on the plunger, a shorting bar having spring means riding the hill-and-valley projection on the plunger and having a contact thereon, and an abutment engaged by the shorting bar during forward motion of the plunger and adapted to push the shorting Vbar over the hill-and-valley projection, the contact on the contact carrier, the shorting bar contact and the xed contact making electrical connection when the plunger moves forward.

2. A switch according to claim 1, in which the contact on the contact carrier is engaged by both the fixed contact and the shorting bar contact when the plunger moves forward. Y

3. A switch according to -clalin l, in combination with a second fixed contact engaged by the 'snorting bar contact when the plunger moves forward. y

4. A switch according to claim 1, in combination with a second contact on the contact carrier engaged by the snorting bar contact when the plunger moves forward and a second rfixed contact engaged by the second contacten the contact carrier when the plunger moves forward.

5. A switch according to claim 1, in combination with a contact making electrical connection with the plunger.

6. A switch according toA claim 1, in which the fixed contact extends radially inwardly into the path of motion of the contact carrier.

7. A switch according tc cla-iin 1, in which a plurality of fixed contacts extend radially inwardly into the path of motion of the Acontact carrier.

8. A switch according to claim 1, in combination with a further xed contact arcuately spaced around the circumference from the 'aforesaid fixed contact and engaged by the contact on the contact carrier during forward movement, and an insulating locating ear extending forwardly from the contact carrier between the fixed contacts, there being electrical connection from the `contact on tne contact carrier to the further `fixed contact including the contact carried by the snorting bar when the contact carrier engages the aforesaid fixed contact.

9. fA 'switch according to claim 1, in which there are a plurality of circumferentially spaced contacts on 'the ycontact carrier electrically -connected to one another, in combination with a second xed contact engaged by one of the contacts on the contact carrier during forward movement, a third fixed contact in one position engaged 'by tne contact on the snorting bar and electrically connected to the second fixed contact and a fourth xed contact in one position engaged by the contact on the snorting bar and electrically connected to the third fixed contact by tne contact of the snorting bar.

10. In a switch, a plunger, a self-adjusting movable contact carrier mounted on the plunger, over-travel means between the contact carrier and the plunger lpermitting the plunger to move further forward after the contact carrier is stopped, a contact mounted on the contact carrier, a fixed contact engaged by the contact on the contact carrier during forward movement, a nill-and-valley projection on the plunger, a snorting bar having spring means riding the hilland-valley projection and having a contact thereon, and an abutment engaged by the shorting bar during forward motion of the plunger and adapted to push the snorting bar over the hill-and-valley projection, the fixed contact, the Contact on the contact carrier and the snorting 'bar contact making electrical connection with one another when the plunger moves forward.

11. A switch according to claim 10, in combination with a second contact mounted on the contact carrier, and engaged by the snorting bar contact when the plunger moves forward.

12. A switch according to claim 10, in combination with a second contact mounted on the contact carrier and engaged by the snorting bar contact as the switch moves forward and a second fixed contact engaged by the second contact on the contact carrier when the plunger moves forward.

13. A switch according to claim 10, in comblnation with a second fixed contact engaged by the contact on tne contact carrier during forward movement, a third lfixed contact engaging the contact 'on tne snorting bar when the plunger moves vforward and electrically connected to the second fixed contact and .a fourth fixed contact engaging the contact on the snorting .bar when the plunger moves forward.

14. In a switch, a plunger having a rearwardly directed shoulder, a self-adjusting movable contact carrier surrounding the plunger and in one position engaging the shoulder, a-spring resiliently urging the contact carrier against 'the shoulder, a contact mounted on the contact carrier, a hilland-valley projection on the plunger, a snorting bar having spring means riding the hill-andvalley projection on tne plunger and having a contact thereon, a fixed contact engaged by the contact on the contact carrier in forward 'motion, an abutment engaging the snorting bar as the plunger is moved forward, and a `further contact engaged by the snorting bar when the short- -ing bar tion, the contact on the contact carrier, the snorting bar contact, the x'ed vcontact and the further contact making electrical connection when the plunger moves forward.

15. A switch according to claim 10, in which the aforesaid contact carrier is electrically conducting, a rearwardly directed shoulder on the plunger is engaged by the contact carrier in one position of the carrier and the aforesaid'contac't carrier is urged against Athe shoulder by a spring, in combination with a second forwardly ldirected contact on `the aforesaid contact 'carrier, both contacts on the aforesaid contact carrier being forwardly directed and being electrically connected to the aforesaid contact carrier, a second electrically conducting Contact carrier on tne plunger angularly disposed at a different position from the first, contacts on the second contact carrier forwardly directed, the second contact carrier in one position engaging the aforesaid contact carrier, a, spring urging the second contact carrier against the aforesaid contact carrier, a second rearwardly directed fixed contact in tne path of movement of one of the contacts on the aforesaid contact carrier and also of one of the contacts on the second contact carrier, a third rearwardly directed fixed contact in the electrically connected to the second fixed contact and a ftn fixed contact forwardly disposed 16. A switch according to claim 10, in which the aforesaid contact carrier is electrically connected to the aforesaid contact electrically conducting contact carrier, a second carrier on the moves over lthe hill-and-valley projec-` aforesaid contact carrier, the 'second contact carrier in one position engaging the aforesaid contact carrier, a spring urging the second contact carrier against the aforesaid contact carrier, a second rearwardly directed fixed contact in the path of movement of one of the contacts on the aforesaid contact carrier on forward travel and also of one of the contacts on the second contact carrier on less advanced forward travel, a third rearwardly directed fixed contact in the path of movement of another contact on the second contact carrier, a fourth fixed contact forwardly disposed in the path of movement of the contact on the shorting bar and electrically connected to the second fixed contact and a fifth fixed contact forwardly disposed in the path of movement of the contact on the shorting bar, and electrically connected to the third fixed contact.

17. A switch according to claim 10, in which the hill-and-valley projection is located on a plunger extension, the aforesaid contact carrier is electrically conducting, a rearwardly directed shoulder on the plunger is engaged by the contact carrier in one position of the carrierV and the aforesaid contact carrier is urged against the shoulder by a spring, in combination with a lost motion connection between the plunger extension and the rest of the plunger including a spring tending to hold the hill-and-valley projection in forward position until the lost motion is taken up, a second forwardly directed contact on the aforesaid contact carrier, both contacts on the .aforesaid contact carrier being forwardly directed and being electrically connected to the aforesaid contact carrier, a second electrically 16 conducting carrier on the plunger angularly disposed at a different position from the first, contacts on the second contact carrier forwardly directed, the second contact carrier in position engaging the aforesaid contact carrier, a spring urging the second contact carrier against the aforesaid contact carrier, a second rearwardly directed fixed contact in the path of movement of one of the contacts on the aforesaid contact carrier and also of one of the contacts on the second contact carrier, a third rearwardly directed first contact in the path of movement of another contact on the second contact carrier, a fourth fixed contact forwardly disposed in the path of movement on the contact on the shorting bar and electrically connected to the second xed contact and a fifth fixed contact forwardly disposed in the path of movement of the contact on the shorting bar and electrically connected to the third xed contact.

JOSEPH H. SCHELLMAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,158,955 Apple et al Nov. 2, 1915 2,359,606 Ballou Oct. 3, 1944 2,363,912 Van Valkenburg Nov 28, 1944 2,447,318 Dazley et al Aug. 17, 1948 2,466,970 Schellman Apr. l2, 1949 FOREIGN PATENTS Number .Country Y Date 78,258 Sweden Mar. 3, 1931- 468,395 Germany Nov. 19, 1928 

